This invention pertains to the art of connecting systems and more particularly to such a system which employs an elongated mechanical fastener which is periodically subjected to bending loads.
The invention is particularly applicable to a system and method for fixedly securing a roller side bearing assembly to a rail car truck assembly and will be described with particular reference thereto. However, it will be appreciated by those skilled in the art that the invention may be readily adapted to use in other applications and environments.
Rail car truck assemblies, i.e., wheel assemblies, are designed to swivel relative to the car itself. Such swiveling is required in order that the trucks may follow the path of the rails. Initially, the trucks were simply pivotally connected to a bottom surface or area of the rail cars with fixed bearing surfaces cooperably interposed between the trucks and car bottom areas. However, frictional forces generated at these bearing surfaces during relative movement between the truck assemblies and their associated cars were greater than desired for achieving optimum operational conditions. It has been determined that these frictional forces and the resultant resistance to swiveling have been primarily responsible for many train derailments, premature wheel flange wear, rail wear and resistance to car movement along the rails.
To overcome the aforementioned problems, the vast majority of new rail cars include or are equipped with roller side bearing assemblies. These bearing assemblies are fixedly secured to the rail car trucks and cooperably interposed between the trucks and associated car bottom area for reducing frictional forces during swivel movement of the trucks. Basically, these roller side bearing assemblies each include an elongated, generally U-shaped bearing cage having a bottom wall fixedly secured to a top surface portion of the associated truck assembly. The bearing assemblies are normally mounted to the laterally extending truck cross member on opposite sides of the truck pivot mounting. One or more cylindrical rollers or bearings is received in the U-shaped cage to extend between spaced apart bearing cage side walls. Roller engagement with the bottom area of the associated rail car produces a rolling action during swivel movement of the truck. Because the coefficient of rolling friction is less than 0.01 and the coefficient of two sliding surfaces of cast or rolled steel is usually greater than 0.25, use of the above described roller side bearing assemblies has greatly reduced the resistance to truck swiveling.
Even though roller side bearings have proved to be extremely advantageous, there have nevertheless been undesired failures occurring at the areas of interconnection between the bearing cages and trucks. Heretofore, the cages have oftentimes been riveted in place. However, during the course of rolling travel of the car, the roller side bearing assemblies are subjected to a wide range of cycle forces which are, in turn, transmitted to the rivets. The cycling forces, particularly bending or shear loads, often cause premature failure therein. Moreover, other types of fastening arrangements which have been attempted have encountered similar failure problems because of the inability to obtain proper loading conditions therein.
For example, and in the case of conventional threaded fasteners such as bolts and the like, they are not capable of withstanding the general type of cyclical bending or shear loads which are applied thereagainst during normal rail car use. As a result, the fasteners fail prematurely and set up an undesirable or improper cooperative relationship between the truck assembly, roller side bearing assemblies and the rail car. Indeed, such failure may establish dangerous operating conditions for the rail car which, if left undetected, could lead to car derailment. When fastener failure is detected, replacement thereof is both costly and time consuming since the rail car must be temporarily removed from further service.
In addition, it is also difficult to consistently obtain the specified or requisite clampload on conventional threaded fasteners. The clampload is obtained by means of applying a torquing force to each fastener or its associated nut in order to obtain tightening or threaded advancement therebetween. However, this torque is neither a measure of nor directly convertible to the amount of clampload obtained. Because of the various frictional forces acting on a threaded fastener or bolt during torquing, i.e., between the bolt head and the surface of the adjacent component, between the threaded bolt shank and an associated nut, and between the nut and the adjacent component, it has heretofore been virtually impossible to correlate the application of some predetermined torque to the resultant loading which is obtained.
Further, conventional threaded fasteners do not include any means for preventing over-tightening. Commonly used assembly tools in rail car shops do not have torque measuring capabilities. Thus, undesired and unacceptable fastener over-tightening is a frequent occurrence. The potential for either under or over-tightened fastener conditions to be present is further increased in the environment of mounting roller side bearing assemblies to rail car trucks because the components involved are fairly large and tend to have fairly rough or uneven surfaces. This then causes the various frictional forces to vary substantially between individual installations.
It has, therefore, been desired to develop a system and/or method for fixedly mounting roller side bearing assemblies to rail car truck assemblies wherein the particular elongated fasteners employed will survive cyclical bending loads applied thereagainst without premature failure and wherein the fasteners include means for preventing over-tightening thereof. Such a system and method should allow fastener installations in a production type situation and permit generally consistent clamploads to be obtained for the individual fastener installations.
The present invention contemplates a new and improved system and method which overcomes all of the above referred to problems and others and provides a mounting system and method for side roller bearing assemblies which is simple, economical, facilitates a fatigue resistant and somewhat torque limiting arrangement, is reliable and which may be adapted to use for a number of different applications.